All-optical precision gunnery simulation (PGS) method and system

ABSTRACT

An all-optical precision gunnery simulation (PGS) system that may be adapted to simulate many tactical gunnery scenarios. The eye-safe system of this invention uses a 1550 nanometer optical infrared (IR) signal to permit increased range and field-of-view (FOV) and reduced scintillation over that of the 904 nanometer IR signals known in the art. Temporal and spatial diversity permit error-free operation over long ranges through dust and scintillation. The system performs all trajectory simulation and hit-miss assessment at the target, thereby permitting the shooter to “fire and forget” without holding station to monitor the target position. The simulation results may be reported to the shooter by passively modulating the retroreflection of an optical return window signal from the shooter. Alternatively, the target may compute shooter position from incoming optical pixel signal data for use in reporting by means of an active narrow-beam optical signal from the target back to the shooter.

CROSS-REFERENCES TO RELATED U.S. PATENT

[0001] This application is related by common inventorship and subject matter to the commonly-assigned U.S. Pat. No. 6,386,879 B1, filed on Mar. 24, 2000 as patent application Ser. No. 09/534,773 by Varshneya et al. under the title “PRECISION GUNNERY SIMULATOR SYSTEM,” which is entirely incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates generally to military training systems and more particularly to a system and method for simulating heavy weapon fire in military training exercises.

[0004] 2. Description of the Related Art

[0005] Explosive-powered artillery has long been classified according to the path or trajectory of its projectile, which is related to the size of the propulsive charge employed. A mortar lobs its shell in a high parabolic path using a relatively light propulsive charge. The shell fired from a cannon or gun, such as a tank gun, is intended for rapid line-of-sight targeting and has an elongate, somewhat level parabolic path and is propelled by a relatively heavy explosive charge. The trajectory of a howitzer shell is a useful compromise, describing a parabolic path of considerable distance but requiring less explosive and a lighter barrel than that of a cannon or gun.

[0006] The United States Military has developed and extensively used the Multiple Integrated Laser Engagement System (MILES) for training ground forces in military operations. Rifles are fitted with low-power lasers and kills are simulated by illuminating a soldier wearing a vest carrying optical detectors. In more elaborate implementations, indirect fire from mortars and howitzers can be simulated, as well as mine fields; in some cases by using player units equipped with Global Positioning System (GPS) receivers. Pyrotechnics and sound may be added to provide enhanced realism to the training exercise.

[0007] Tanks remain a very important element of ground assault operations. Any laser-based gunnery system for simulating cannon fire from a tank must account for the trajectory of a real projectile, such as a one-hundred-and-twenty millimeter shell, which requires substantial time to move from the tank to the target or target area. In contrast, a laser beam moves in a straight line at the speed of light. Numerous gunnery training systems have been developed such as those disclosed in U.S. Pat. No. 4,218,834 entitled SCORING OF SIMULATED WEAPONS FIRE WITH SWEEPING FAN-SHAPED BEAMS and issued to of Robertson. Robertson discloses a gunnery training system designed to accurately simulate tank fire in complex tactical situations. Horizontally-sweeping fan-shaped beams of laser radiation are emitted at or about the instant of simulated cannon fire. These fan-shaped beams are employed to measure the range, azimuth and elevation of a target by receiving and processing reflections from the target. During this scanning period, a theoretical calculation is made of the instantaneous position in terms of range, azimuth and elevation of a simulated projectile. The relationship between the simulated projectile position and the angular position of each scan beam upon its interception by the retro-reflector is also calculated. The scoring instant is determined when the weapon-to-reflector distance equals the weapon-to-projectile distance, or when the projectile is computed to be at a predetermined elevation relative to the target. Scoring is based on the relationship of the theoretical projectile position to the reflected angular beam position at the scoring instant. Scoring results are displayed in the shooter tank and/or transmitted to the target using beam-modulation for use in evaluating the effect of the simulation at the target. Disadvantageously, the shooter tank must hold-station during the projectile transit period to permit continuous scanning of the target.

[0008] In the above-referenced commonly-assigned U.S. Pat. No. 6,386,879 B1 (patent application Ser. No. 09/534,773), Varshneya el al. disclose a gunnery simulation system having a gun with laser in its muzzle that emits a beam of optical radiation responsive to a trigger pull. The laser beam is directed toward a target by the shooter's conventional ranging and tracking system. The target is then scanned with the beam of radiation to measure a target azimuth and a target elevation with respect to a boresight of the gun. The trigger pull time is also transmitted to the target. Optical receivers at the target detect the laser beam illuminating the target and a system control unit at the target determines the target azimuth and target elevation (relative to the shooter boresight) from information encoded in the arriving laser beams. The target system control unit also determines a range to the target by comparing a set of GPS coordinates of the gun (received from the shooter) and the target. Based on the target azimuth, the target elevation, the range to the target and the time of the trigger pull, the target system control computes the simulated impact point on the target of a simulated ballistic shell fired from the gun at the time of the trigger pull. This system advantageously permits the shooter to “fire and forget” without holding station to monitor the target position because all target position detections and simulation computations may be performed at the target. However, the target computations may require 2-6 seconds and must be reported to the shooter by some means, usually by means of a tactical radio-frequency (RF) link. Other disadvantages include the limited simulation range arising from the laser power limits imposed to comply with eye-safety requirements and the limited exercise participation arising from the limited RF link channel capacity.

[0009] There is accordingly a clearly-felt need in the art for further enhanced realism of the tank gunnery training exercises in complex tactical situations, such as longer ranges for simulating improved cannons and more participation capacity in single exercises for simulating complex tactical situations involving large numbers of tanks. These unresolved problems and deficiencies are clearly felt in the art and are solved by this invention in the manner described below.

SUMMARY OF THE INVENTION

[0010] This invention solves the above problems by introducing an all-optical precision gunnery simulation (PGS) system that for the first time may be adapted to simulate many tactical gunnery scenarios. The eye-safe PGS system of this invention uses a 1550 nanometer optical infrared (IR) signal to provide increased range and field-of-view (FOV) and reduce scintillation over that of the 904 nanometer IR signal known in the art.

[0011] It is a purpose of this invention to provide a PGS system that can simulate engagement at longer ranges, up to 4 km and more with eye-safe optical signal intensities. It is an advantage of this invention that it provides a PGS system that can operate in battlefield smoke and haze at eye-safe signal levels.

[0012] It is another purpose of this invention to provide a PGS system that does not require radio-frequency (RF) return links to report the target effects of simulated gunnery. It is an advantage of the all-optical system of this invention that no RF channels are required to complete a gunner simulation, thereby removing a well-known channel limitation on the number of participants in a simulated battlefield.

[0013] It is an important purpose of this invention to provide a PGS system with improved range and FOV by adding simple and inexpensive components and firmware changes to an existing PGS system such as the one disclosed in the above-cited Varshneya et al patent. It is an advantage of the PGS system of this invention that substantial range and data rate improvements are accomplished with the addition of simple components (such as retroreflectors, obturators and upgraded laser transmitters and detectors) and firmware revisions to a PGS system presently known in the art.

[0014] The PGS system of this invention permits all trajectory simulation and hit-miss assessment to be performed at the target, thereby advantageously permitting the shooter to “fire and forget” without holding station to monitor the target position. The simulation results may be returned to the shooter by passively modulating the retroreflection of an optical return window signal from the shooter. Alternatively, the PGS system of this invention permits the target to determine shooter position precisely from incoming optical pixel signal data for use in transmitting an active narrow-beam optical signal from the target back to the shooter if desired.

[0015] In one aspect, he invention is a method for simulating the effects on a target of firing a ballistic projectile from a gun at a trigger pull time, the target including a retroreflector and the gun including a muzzle adapted to support an optical transmitter, including the steps of (a) illuminating the target with an optical pixel signal emitted from the optical transmitter and encoded to represent its emission angle with respect to the muzzle and global positioning system (GPS) coordinates for the gun, (b) receiving the optical pixel signal at the target, (c) producing target azimuth and elevation angles with respect to the gun corresponding to the optical pixel signal emission angle, (d) producing a target range corresponding to the GPS coordinates for the gun with respect to GPS coordinates for the target, and (e) producing a hit-miss decision representing the simulated ballistic projectile effects on the target.

[0016] In another aspect, the invention is a PGS transmitter assembly for use in a PGS system for simulating the effects on a target of firing a ballistic projectile at a trigger pull time from a gun having a muzzle, including optical transmitter means fixed to the muzzle for emitting an optical pixel signal and an optical return window signal, transmit controller means coupled to the optical transmitter means for encoding the optical pixel signal to represent its emission angle with respect to the muzzle and GPS coordinates for the gun, optical detector means fixed to the gun for receiving a reflected optical return window signal from a target retroreflector, and decoder means coupled to the optical detector means for producing target azimuth and elevation angles corresponding to the reflected optical return window signal.

[0017] In yet another aspect, the invention is a PGS target assembly for use in a PGS system for simulating the effects on a target of firing a ballistic projectile at a trigger pull time from a gun having a muzzle, including retroreflector means for reflecting an incoming optical signal generally back along the incoming path thereof, optical detector means for receiving an optical pixel signal encoded to represent its emission angle with respect to the muzzle and GPS coordinates for the gun. decoder means coupled to the optical detector means for producing target azimuth and elevation angles corresponding to the optical pixel signal emission angle, ranging logic means coupled to the decoder means for producing a target range corresponding to the GPS coordinates for the gun with respect to GPS coordinates for the target, and simulation controller means coupled to the decoder means and the ranging logic means for producing a hit-miss decision representing the simulated ballistic projectile effects on the target.

[0018] In an exemplary embodiment, the invention is a PGS system for simulating the effects on a target of firing a ballistic projectile at a trigger pull time from a gun having a muzzle, including a PGS transmitter assembly having an optical transmitter fixed to the muzzle for emitting an optical pixel signal and an optical return window signal, a transmit controller coupled to the optical transmitter for encoding the optical pixel signal to represent its emission angle with respect to the muzzle and GPS coordinates for the gun, a first optical detector fixed to the gun for receiving a reflected optical return window signal from the retroreflector, and a first decoder coupled to the first optical detector for producing target azimuth and elevation angles corresponding to the reflected optical return window signal; and a PGS target assembly having a retroreflector for reflecting an incoming optical signal generally back along the incoming path thereof, a second optical detector for receiving an optical pixel signal encoded to represent its emission angle with respect to the muzzle and GPS coordinates for the gun, a second decoder coupled to the second optical detector for producing target azimuth and elevation angles corresponding to the optical pixel signal emission angle, a ranging logic coupled to the second decoder for producing a target range corresponding to the GPS coordinates for the gun with respect to GPS coordinates for the target, and a simulation controller coupled to the second decoder and the ranging logic for producing a hit-miss decision representing the simulated ballistic projectile effects on the target.

[0019] The foregoing, together with other objects, features and advantages of this invention, can be better appreciated with reference to the following specification, claims and the accompanying drawing.

DESCRIPTION OF THE DRAWINGS

[0020] For a more complete understanding of this invention, reference is now made to the following detailed description of the embodiments as illustrated in the accompanying drawing, in which like reference designations represent like features throughout the several views and wherein:

[0021]FIG. 1A illustrates two tanks in a simulated engagement using the all-optical precision gunnery simulation (PGS) system and method of this invention;

[0022]FIG. 1B is a perspective diagram illustrating in detail the muzzle-mounted transmitter assembly portion of the PGS transmitter system of this invention;

[0023]FIG. 1C is a schematic diagram illustrating the retroreflector and obturator element of the PGS target system of this invention;

[0024]FIG. 1D is a schematic diagram illustrating the retroreflector and obturator element of the PGS target system of this invention;

[0025]FIG. 2 is a block diagram of an exemplary embodiment of the electronics system elements mounted in each tank in accordance with the system of this invention;

[0026]FIG. 3 is a block diagram of an exemplary embodiment of a PGS transmitter assembly in accordance with this invention;

[0027]FIG. 4 is a block diagram of an exemplary embodiment of a PGS target assembly in accordance with this invention;

[0028]FIG. 5 is a block diagram of an exemplary embodiment of a PGS system in accordance with this invention;

[0029] FIGS. 6A-6D are timing diagrams illustrating an exemplary optical signal pulse coding and signal timing method suitable for use with the system of this invention;

[0030]FIG. 7 is a flowchart diagram illustrating an embodiment of the method of this invention; and

[0031]FIG. 8 is a flowchart diagram illustrating a detailed embodiment of a reporting step from FIG. 7.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032]FIG. 1A illustrates the functional architecture of a preferred embodiment of the all-optical precision gunnery simulator (PGS) system of this invention. A first friendly tank or shooter 10 is shown engaging and firing its gun 12 upon a second enemy tank or target 14. Shooter 10 is at a first location and the target 14 is at a second location that may typically be several hundred meters from the first location. It should be understood that one or both of tanks 10 and 14 may be stationary or moving at speeds of sixty kilometers per hour or more. Gun 12 of shooter 10 is mounted on a stabilized turret 16 in any useful conventional fashion. Similarly, the gun 18 of enemy tank 14 is similarly mounted on a stabilized turret 20. By way of example, tanks 10 and 14 may be M1A1 main battle tanks with 120 millimeter guns having a normal firing range of 3,500 meters (with SABOT munition) and 2,500 meters (with HEAT munition).

[0033] As shown in FIG. 1B, each of tanks 10 and 14 has mounted on its gun muzzle 22 a data link antenna 24 and a global positioning system (GPS) antenna 26. Each of the tanks 10 and 14 also has a laser scanner transmitter 28 mounted in the bore of gun muzzle 22. A cable 30 operatively connects the data link antenna 24, GPS antenna 26 and laser scanner transmitter 28 to system electronics (FIG. 2) carried inside the turret 16 or hull 32 of the associated tank. GPS antenna 26 mounted on gun muzzle 22 of each tank receives downlink geographic locating signals from a plurality of the twelve Earth-orbiting GPS satellites, exemplified by the GPS satellites 34 and 36 shown in FIG. 1A. Optionally, more precise geographic locating signals in the form of DGPS correction signals are transmitted to GPS antenna 26 of each of the tanks 10 and 14 by a ground-based GPS reference station 38 seen in FIG. 1A. GPS reference station 38 receives downlink locating signals from the satellites 34 and 36 and computes the local DGPS correction by comparing the location encoded in the downlink locating signals to the known location of station 38. Optionally, GPS reference station 38 may relay radio frequency (RF) data between the tanks 10 and 14 and a command station 40 for purposes such as providing reports, monitoring engagements or controlling the PGS system in some way, such as providing mission protocol changes.

[0034] Preferably antennas 24 and 26, laser scanner transmitter 28 and cable 30 are adapted to be readily installed and removed without interfering with the normal firing of live rounds so that tanks 10 and 14 are always ready for real battle. Laser scanner transmitter 28 emits a beam of optical radiation, preferably infrared (IR) at about 1550 nanometers, that is used to scan the position of an opposing tank, in a scan pattern 31 made up of a two-dimensional array of optical pixel signals, for example, and to transfer information to the opposing tank for use in computing the simulated effects of firing a simulated round.

[0035]FIG. 2 is a block diagram of an exemplary embodiment of the electronics preferably mounted in the crew compartment of each tank 10 and 14 in accordance with the PGS system of this invention. A system control unit 42 forms the core of the electronics. Control unit 42 has its own power supply and is preferably microprocessor-based. Control unit 42 includes ample memory for storing a firmware operational program that provides the sequence of steps necessary for performing the method of this invention. Preferably system control unit 42 has a keyboard or other input device 43 connected thereto by way of a fire control computer (FCC) 44 for accepting crew input commands. Input device 43 accepts specifications such as ammo type, Met data, inertial data, and so forth as entered by the crew. Input device 43 preferably has a trigger switch (not shown) that may be pulled by the crew to fire a simulated round and to communicate a “trigger pull (TP) time” to system control unit 42, for example. Input device 43 and FCC 44 functionality may be provided by existing tank hardware or may be embodied as parallel devices that simulate such actual tank counterparts. A removable media storage device (not shown) is preferably connected to system control unit 42 to facilitate loading of changes in the firmware and operational program. The power supply of the control unit 42 derives its power from the vehicle power supply 45.

[0036] For completeness, FIG. 2 also shows a kill strobe 46 and a flash-bang generator 48 that may be activated by system control unit 42. Many other useful items such as, for example, audio speakers and audio amplifiers (not shown) and smoke generators (not shown) may be connected to system control unit 42 to enhance realism of the simulated tank battle. An optional Met sensor 50 may also be connected to system control unit 42. GPS antenna 26 is connected to system control unit 42 through a DGPS receiver 52. Data link antenna 24 is connected to system control unit 42 by way of a CTC data link transceiver unit 54 and a PGS data link transceiver unit 56. DGPS correction signals from GPS reference station 38 are received by way of data link antenna 24 and are coupled through CTC data link transceiver unit 54 to DGPS receiver 52. Laser scanner transmitter 28 is driven by a laser scanner, interrogator and data link circuit 58 under control of system control unit 42. The gunner's primary sight 60 includes a lens assembly 62 and has a tracer overlay 64 that communicates with the system control unit 42 by way of the tracer overlay drive circuit 66.

[0037] As shown in FIG. 1A, a first optical array 68 of elements is spaced around tank turret 16. A second optical array 70 of elements is spaced around the tank hull 32. As shown in FIG. 1C, each optical element of arrays 68 and 70 includes an optical detector 71 or a retroreflector 73 or both. Each detector 71 may include a lens exemplified by the lenses 68 a and 70 a (FIG. 2) and a translucent protective cover exemplified by the covers 68 b and 70 b, for example. Each retroreflector 73 may include an obturator exemplified by the obturators 68 c and 70 c (FIG. 2), for example, each obturator being subject to an obturator control signal 77. Optical detectors 71 each generate electrical signals for transmission to system control unit 42 when illuminated by the optical beam from laser scanner transmitter 28 of an opposing tank. As shown in FIG. 1A, the elements of optical arrays 68 and 70 are spaced about the turret and hull to detect a laser scan or simulated laser projectile from any angle within the range of generally 360 degrees in azimuth and generally from 75 degrees above the horizon to 15 degrees below the horizon in elevation. This field of view (FOV) is sufficient to permit simulated engagement with helicopters as well as other tanks, for example.

[0038] A turret orientation sensor 72 (for example, an optical encoder), an inertial unit 74 and a hull orientation sensor 76 all provide corresponding data signals to system control unit 42. A target-only module 78, a shooter-only module 80, a shooter and target module 82 and an external system module 84 may optionally be connected to system control unit 42.

[0039]FIGS. 1C and 1D illustrate in more detail an exemplary optical array element 68 including optical detector 71 and retroreflector 73. Retroreflector 73 provides for the precision return along the incoming path of any ray arriving from a direction within a 90 degree cone of coverage and may include the obturator 75 for blocking such reflection responsive to obturator control signal 77. Alternatively, optical array 68 may include a plurality of detectors 71 and a plurality of retroreflectors 73 in alternating disposition every 45-degrees of azimuth and distributed in elevation to provide the desired 360-degree hemispherical coverage from 75 degrees above the horizon to 15 degrees below the horizon. Optical array elements 68 and 70 are fixed to the tank surface by any useful means, such as, for example, cement (not shown), and may be oriented asymmetrically with respect to the vertical axis to enhance the desired hemispherical coverage above the horizon and down to 15 degrees below the horizon. Retroreflector 73 may employ any useful retroreflector device known in the art, such as, for example, one of the line of Tech Spec™ Corner Cube Retroreflectors (Trihedral Prisms) available from Edmond Industrial Optics, Barrington, N.J. Obturator 75 may include a mechanical shutter device capable of cycling open and closed within a few milliseconds, or more preferably, a liquid crystal device (LCD) disposed over the retroreflector portion, such as the LCD-CDS92106 available from Cubic Defense Systems, San Diego, Calif., for example, which can cycle within milliseconds between opaque and translucent states responsive to obturator control signal 77.

[0040] The PGS system of this invention may be adapted to provide tank fire simulation in any of four modes of tank operation known in the art. These modes are Normal, Degraded, Emergency and Manual shooting modes. In operation, before the TP, the shooter performs certain ranging and tracking functions that depend on the operational mode of the tank. The shooter first lays the main crosshair on target, ranges the target by means of a laser signal, lays once again on target for firing, and pulls the trigger. In the Normal mode, the gun turret orientation is controlled automatically by the electronic system shown in FIG. 2. All aiming data are derived from sensor inputs and the platform is fully stabilized. After laying on the target, the shooter merely pulls the trigger without concern for own-tank motion. Similarly, in the Emergency mode, all aiming data are derived from sensors but the shooter must halt to shoot because the stabilization system is presumed non-functional. But the shooter again merely lays on target and pulls the trigger after halting own-tank movement. The Degraded mode retains platform stabilization but loses some or all of the sensor data normally available to the fire control system. In Degraded mode, the shooter must manually enter the missing sensor data into the control system before pulling the trigger, but need not halt the tank. Finally, in the Manual mode, the shooter has lost all control systems, including the turret motors. In Manual mode, the shooter must aim and shoot the gun using hand-cranking devices and passive optics.

[0041] In the automated shooting modes, the shooter ranges target tank 14 by scanning the target tank 14 with a sequence of optical pixel ranging signals from laser scanner transmitter 28, each encoded with minimal data such as a pixel beam number (representing pixel AZ and EL with respect to the boresight axis of the gun), and the shooter ID code. The shooter FOV is large enough to accommodate any of the ammunition types that can be fired by tank 10. Some of the pixel ranging signals in scan pattern 31 then illuminate target tank 14. Each pixel ranging signal that illuminates target tank 14 is passively reflected by one or more retroreflectors 73 and returned to shooter tank 10 where the reflection is detected and decoded. The decoded reflection is validated by examining the shooter ID and the range to target tank 14 may be computed by, for example, comparing the time of reflection arrival to the transmission time of the ranging pixel signal of the same beam number. Target aiming and tracking are then carried out according to the particular shooting mode in the conventional fashion by the FCC 44 and this generates the required gun lead and elevation, for example.

[0042] In any of the shooting modes, at TP time, the shooter again lays on target tank 14 and pulls the trigger. Laser scanner transmitter 28 again optically scans target tank 14 with a sequence of optical pixel TP signals distributed over scan 31. But each of these optical pixel TP signals is encoded with data representing the entire disposition of shooter tank 10. Pixel TP data include, for example, the TP time, the shooter ID, the weapon type, the ammo type, the gun tilt and twist angles, the GPS (x, y, z) position data, the GPS (Vx, Vy, Vz) velocity data, a pixel beam number pixel TP signals in scan pattern 31 then illuminate target tank 14. Each pixel TP signal that illuminates target tank 14 is received at optical detectors 71 in arrays 68-70 and the pixel data are decoded by electronics in the target tank 14 (FIGS. 2, 5), which are the same as those in the shooter tank 10. Target tank 14 determines the target AZ and target EL with respect to the shooter's boresight, by knowing the TP time and pixel scan rate or by decoding the angular position data encoded in the pixel signal, for example. The range from shooter tank 10 to target tank 14 at TP time is determined by comparing the contemporaneous shooter and target GPS coordinates, for example. The orientation of the entire shooter and target geometry with respect to gravity is determined from the DGPS or from tilt and twist sensors 72, 74 and 76, for example.

[0043] With these data, system control unit 42 in target tank 14 may execute a ballistic simulation to compute the projectile impact coordinates. The projectile AZ and super EL at TP time with respect to the shooter boresight are derived from the pixel beam number or scan timing data. Target tank 14 tracks its own motion during the simulated fly-out time of about two to three seconds by means of DGPS and carrier phase information. With this simulation, system control unit 42 in target tank 14 determines the impact point of the simulated projectile within six to ten seconds after TP time and makes a hit-miss decision. If a miss is determined, the weapon/target perigee is determined and the crew of the target tank 14 is informed of the results of the enemy fire, preferably by intercom, and simulated collateral damage is assessed. If a hit is determined, the shot aspect angle is calculated from optical detector and turret encoder data. System control unit 42 then performs a casualty assessment in accordance with the simulated impact coordinates, range, shot aspect angle, known weapon/target vulnerability data and so forth. System control unit 42 then notifies shooter tank 10 by means of kill strobe 46 and. Pk, range and hit coordinates are displayed on a display 86 (FIG. 2) in the shooter tank's crew cabin.

[0044] A simplified projectile fly-out simulation is also performed by system control unit 42 in shooter tank 10. This permits a projectile fly-out tracer display to the shooter on tracer overlay 64 in gunner's sight 60. Compensation is made for the motion of shooter tank 10 during the projectile fly-out interval. Sufficient data is recorded by means of, for example, a camera (not shown) to support a diagnostic after-action review (AAR).

[0045] The PGS system and method of this invention are now described in more particular detail. FIG. 3 is a block diagram of an exemplary embodiment of a PGS transmitter assembly 88 in accordance with this invention. Although assembly 88 is illustrated as part of circuit 58 in FIG. 2, much of the functionality of assembly 88 may be instead embodied within, for example, system control unit 42. The infrared (IR) laser diode 90 emits a coherent beam 92 of IR radiation that is redirected by the scanning mirror 94, which is rotated about an axis by the motor 96. Although shown with a single axis, scanning mirror 94 is preferably moveable about two axes to permit redirection of beam 92 in both AZ and EL under the control of a scan controller 98. The transmitter simulation controller 100 accepts data from system control unit 42 representing GPS coordinates, TP time, etc., for use in creating the optical pixel signals of this invention. The pixel encoding is then passed to the pixel encoder 102, which operates laser diode 90 to create the optical pixel signals in beam 92. The IR detector 104, which may be embodied as single detector or as a detector array, for example, accepts an incoming optical signal 106. Signal 106 may be a reflected pixel signal returning from a target or an active optical signal from the target, for example. IR Detector 104 passes optical signal 106 to a signal decoder 108, which operates to decode and transfer any pixel data present in optical signal 106 to system control unit 42. The features of the optical pixel signals and data encoding method of this invention are further described below in conjunction with FIGS. 6A-6D.

[0046]FIG. 4 is a block diagram of an exemplary embodiment of a PGS target assembly 110 in accordance with this invention. Although assembly 110 is illustrated as part of optical arrays 68-70 in FIG. 2, much of the functionality of assembly 110 may be embodied within, for example, system control unit 42. Beam 92 arrives at detector 71 and is passed to the pixel decoder 112, which extracts the data embodied in the arriving pixel signal. These pixel data are then passed to a ranging logic 114 and to a target simulation controller 116 for use in computing the range from shooter tank 10 to target tank 14 and for extracting the AZ and EL angles of beam 92 with respect to the boresight axis of the gun on shooter tank 10, for example. Logic 114 and controller 116, in cooperation with system control unit 42, accept the pixel data and perform the necessary trajectory simulation to arrive at the simulated projectile impact coordinates. These coordinates are examined to make a hit-miss decision, which is then reported to the crew of target tank 14 for use in standing down or continuing the exercise, as appropriate. Because all simulations are performed in assembly 110 at target tank 14, shooter tank 10 does not require any information about the disposition of target tank 14 after TP time. This “shoot-and-forget” feature of the system of this invention is available during simulation of any of the four shooter modes described above.

[0047] Retroreflector 73 may operate to passively reflect beam 92 as reflected beam 106, which may be detected at shooter tank 10 for use as described above (FIG. 3). Optionally, obturator 75 is provided to block reflection from retroreflector 73 under control of an obturator modulator 118. For example, after completing the TP pixel signal scan, shooter tank 10 may transmit an optical return window signal on beam 92 following a delay sufficient to account for the simulation fly-out and computation time of six to ten seconds. This return window signal may be and is preferably encoded to inform controller 116 of the identity of the sender and the purpose of the signal. The response encoder 120 may then be commanded to encode useful data (such as the hit-miss decision and impact coordinates) and pass them to modulator 118 for use in opening and closing obturator 75 to selectively modulate reflection 106 with the encoded information. Modulated reflection 106 may then be received and decoded at assembly 88 of tank 10 in the manner described above (FIG. 3). Any useful pulse-code modulation (PCM) scheme known in the art may be adapted for use with this aspect of assemblies 88 and 110 such as, for example, the asynchronous pulse code described below in connection with FIGS. 6A-6D.

[0048]FIG. 4 also shows an active optical reporting system 88A, which provides an active optical alternative to the functionality of the passive modulated retroreflector reporting system shown in assembly 110. System 88A is shown as providing both the functionality of assembly 88 (FIG. 3) and the functionality of an active optical reporting system. Alternatively, system 88A may be separately embodied and independent of the functionality of assembly 88, for example. Scanning mirror 94 may be positioned to direct the narrow beam 92A directly to shooter tank 10 by using the GPS data on the pixel signals received therefrom at beam 92, for example. Either of these passive and active optical reporting methods eliminates the problems associated with using battlefield RF links for reporting simulation results.

[0049]FIG. 5 is a block diagram of an exemplary embodiment of a PGS system 122 in accordance with this invention suitable for installation in each tank. PGS system 122 includes both assemblies 88 and 110 to permit operation as both shooter and target during precision gunnery simulation exercises. Of course, the functionality of many elements in system 122 may be combined or segregated as desired for effective implementation and the organization illustrated herein is merely exemplary and is presented for expository purposes.

[0050] FIGS. 6A-6D are timing diagrams illustrating an exemplary optical signal pulse coding and signal timing method suitable for use with the system of this invention. FIG. 6A shows an exemplary ranging pixel code 124 arranged as a framed sequence of 200 ns pulse bins. Code 124 includes a preamble frame 126 with three pulses, a beam number frame 128 with one pulse, and a double shooter ID frame 130 with two pulses. Preamble frame 126 includes 273 bins and encodes one of 180 possible values by positioning three pulses. Beam number frame 128 includes 349 bins and encodes one of 256 possible values (8 bits) by positioning a single pulse. Each of ID frames 130 include 125 bins and encode one of 32 values (10 bits total for both frames) by positioning a single pulse within each frame. Using 50 ns pulses, the duty cycle of laser diode 90 is about 0.2 percent and the entire pixel ranging code can be completed in less than 175 microseconds. Preferably, each optical pixel signal in beam 92 illuminates 0.4 milliradians (about 1.4 meters at full range) and is scanned over a range of minus 35.5 to plus 35.5 milliradians (about 250 meters at full range) in AZ and EL.

[0051]FIG. 6B shows an exemplary TP pixel code 132 arranged as a framed sequence of 200 ns pulse bins. Code 124 begins with the same preamble, beam number and ID frames shown in code 124 (FIG. 6A) and continues with 13 identical data frames, exemplified by the data frame 134, each having one pulse. Data frame 134 includes 157 bins and encodes one of 64 possible values (6 bits) by positioning a single pulse. The data frames may, for example, be assigned to transfer 6-bit values for shooter tank parameters such as cant, crosswind, ammo, GPS (x, y, z), GPS (Vx, Vy, Vz), TP time, etc. Using 50 ns pulses, the duty cycle of laser diode 90 is less than 0.2 percent and the entire pixel TP code can be completed in less than 600 microseconds. Preferably, each optical pixel signal in beam 92 illuminates 0.4 milliradians (about 1.4 meters at full range) and is scanned over a range of minus 35.5 to plus 35.5 milliradians (about 250 meters at full range) in AZ and EL.

[0052]FIG. 6C shows the sequential repetition of each pixel sequence as beam 92 is scanned in AZ. Each pixel code is preferably repeated four times in scan sequence to overcome possible data loss from atmospheric scintillation. This may be accomplished by limiting the scan rate to less than 0.1 milliradians per pixel code sequence (about 30 degrees per millisecond for ranging signals and about 10 degrees per millisecond for TP signals) so that the four repeated beam numbers on a 0.4 milliradian beam 92 illuminate the same spot. In FIG. 6C, the beam #1 pixel code is shown as repeated four times as the 4-milliradian beam 92 scans slowly across four milliradians. It may be readily appreciated that a sensor 136 disposed as shown is illuminated by each of the four repeated beam # 1 pixel codes; by the right edge of the first one and by the left edge of the last. As the beam #2 pixel code transmission begins, beam 92 has moved beyond sensor 136 into the adjacent region 138. The temporal diversity provided by this repeated illumination of sensor 136 introduces useful redundancy into the decoding effort in assembly 110, thereby significantly improving recovery from data errors arising from atmospheric scintillation. The spatial diversity provided by having more than one optical detector 71 in arrays 68-70 (FIG. 1A) also adds useful redundancy to the decoding effort in assembly 110.

[0053]FIG. 6D illustrates the entire PGS simulation sequence discussed above. In the tracking phase 140, shooter tank 10 may scan target tank 14 for ranging and to set up a shot. At the TP time 142, the pixel TP signal scan is performed in response to the trigger pull operation by the shooter and all scanning stops as shooter tank “shoots and forgets” to proceed with other activities as desired. During the fly-out phase 144, target tank 14 initiates and proceeds with a ballistic simulation, which continues after impact (at up to 2 seconds) into the post-impact phase 146 as necessary to complete all calculations (2-6 seconds). Finally, in the reporting phase 148, shooter tank 10 may illuminate target tank 14 with a return window signal for passive modulated reflection reporting or target tank 14 may actively report by illuminating shooter tank 10 at a location deduced from the GPS location and velocity data reported during the pixel scan in interval 140. The reporting methods may also be used during the ranging scan (before TP) when Target tank 14 determines (from shooter ID data) that shooter tank 10 is actually friendly instead of enemy. A range computation may be made and returned by target tank 14 under such circumstances, for example.

[0054]FIG. 7 is a flowchart diagram illustrating an embodiment of the method of this invention for precision gunnery simulation. In the first step 150, the shooter pulls the trigger to produce a TP time. In the next step 152, the shooter tank emits optical pixel signals to illuminate the target tank. In step 154, one of the pixel signals is detected at the target tank and is decoded at the step 156 to produce pixel data such as shooter AZ and EL, GPS data, TP time, and so forth. In the step 158, the range from shooter to target is computed at the target tank. In step 160, the ballistic simulation is completed to compute the simulated projectile impact coordinates. These impact coordinates are assessed in the step 162 to determine the effects of the simulated projectile on the target tank. Finally, in the step 164, these effects are reported back to the shooter tank, preferably by passive or active optical signaling.

[0055]FIG. 8 is a flowchart diagram illustrating an exemplary passive optical embodiment of the reporting step 164. In the first step 166, the shooter tank illuminates the target tank with an optical return window signal, which is preferably encoded to notify the target tank of the identity and purpose of the signal. In the next step 168, the target tank certifies the identity and purpose of the return window signal and, in the step 170, the target tank modulates the obturator to selectively reflect the return window signal back to the shooter tank. In the step 172, the modulated reflection is detected at the shooter tanks and, in the final step 174, it is decoded to yield the report sent from the target tank.

[0056] Other significant features of the PGS system of this invention include the use of 1550 nanometer IR radiation to better penetrate dust and smoke. Because 1550 nm IR is much more eye-safe than the 904 nm radiation used in the art, engagement may now be simulated at longer ranges (up to 3750 meters) because power levels may be increased while retaining Class 1 eye safety. Elimination of the RF reporting link is facilitated for the first time by means of the optical reporting methods of this invention, thereby eliminating channel collisions during battle simulation exercises. The 1550 nm IR detection systems of this invention are backward compatible with earlier 904 nm systems. Finally, helicopter engagement simulations may be implemented using the passive optical modulation features of the PGS system of this invention with the addition of smaller InGaS optical detectors to cover a 360×45 degree FOV.

[0057] Clearly, other embodiments and modifications of this invention may occur readily to those of ordinary skill in the art in view of these teachings. Therefore, this invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawing. 

I claim:
 1. A method for simulating the effects on a target of firing a ballistic projectile from a gun at a trigger pull time, the target including a retroreflector and the gun including a muzzle adapted to support an optical transmitter, the method comprising the steps of: (a) illuminating the target with an optical pixel signal emitted from the optical transmitter and encoded to represent its emission angle with respect to the muzzle and global positioning system (GPS) coordinates for the gun; (b) receiving the optical pixel signal at the target; (c) producing target azimuth and elevation angles with respect to the gun corresponding to the optical pixel signal emission angle; (d) producing a target range corresponding to the GPS coordinates for the gun with respect to GPS coordinates for the target; and (e) producing a hit-miss decision representing the simulated ballistic projectile effects on the target.
 2. The method of claim 1 further comprising the step of: (a.1) scanning the target with a sequence of optical pixel signals each emitted from the gun at one of a plurality of predetermined emission angles.
 3. The method of claim 2 wherein the retroreflector includes an obturator, further comprising the steps of: (f) illuminating the target with an optical return window signal transmitted from the optical transmitter; (g) selectively reflecting the optical return window signal back along the line of incidence by opening and closing the retroreflector obturator according to a response code representing the hit-miss decision for the simulated ballistic projectile.
 4. The method of claim 3 further comprising the step of: (e.1) producing at the target simulated projectile impact coordinates corresponding to the target azimuth and elevation angles, the target range and the trigger pull time.
 5. The method of claim 2 further comprising the step of: (a.1) encoding each optical pixel signal with a sequential beam number corresponding to a predetermined angle with respect to the muzzle.
 6. The method of claim 1 further comprising the step of: (a.1) encoding the optical pixel signal to represent the trigger pull time.
 7. The method of claim 1 wherein the optical pixel signal is emitted at an infrared (IR) wavelength in the range from generally 1500 to generally 1600 nanometers.
 8. The method of claim 2 wherein the target includes a second optical transmitter, further comprising the step of (f) illuminating the gun with an optical signal emitted by the second optical transmitter and encoded to represent the hit-miss decision.
 9. The method of claim 8 further comprising the step of: (e. 1) producing at the target simulated projectile impact coordinates corresponding to the target azimuth and elevation angles, the target range and the trigger pull time.
 10. A precision gunnery simulation (PGS) transmitter assembly for use in cooperation with a PGS target assembly having a retroreflector in a PGS system for simulating the effects on a target of firing a ballistic projectile at a trigger pull time from a gun having a muzzle, the PGS transmitter assembly comprising: optical transmitter means fixed to the muzzle for emitting an optical pixel signal and an optical return window signal; transmit controller means coupled to the optical transmitter means for encoding the optical pixel signal to represent its emission angle with respect to the muzzle and global positioning system (GPS) coordinates for the gun; optical detector means fixed to the gun for receiving a reflected optical signal from the retroreflector; and decoder means coupled to the optical detector means for recovering data from the reflected optical signal.
 11. The PGS transmitter assembly of claim 10 further comprising: a scanning encoder coupled to the optical transmitter means for encoding a sequence of optical pixel signals each emitted from the gun at one of a plurality of predetermined emission angles.
 12. The PGS transmitter assembly of claim 11 further including: a beam number encoder coupled to the transmit controller means for encoding the optical pixel signal with a sequential beam number corresponding to a predetermined angle with respect to the muzzle.
 13. The PGS transmitter assembly of claim 10 further comprising: a trigger pull encoder coupled to the transmit controller means for encoding the optical pixel signals to represent the trigger pull time.
 14. The PGS transmitter assembly of claim 10 wherein the optical transmitter means includes means for emitting infrared (IR) energy having a wavelength in the range from generally 1500 to generally 1600 nanometers.
 15. A precision gunnery simulation (PGS) target assembly for use in cooperation with a PGS transmitter assembly in a PGS system for simulating the effects on a target of firing a ballistic projectile at a trigger pull time from a gun having a muzzle, the PGS target assembly comprising: retroreflector means for reflecting an incoming optical signal generally back along the incoming path thereof, optical detector means for receiving an optical pixel signal encoded to represent its emission angle with respect to the muzzle and global positioning system (GPS) coordinates for the gun; decoder means coupled to the optical detector means for producing target azimuth and elevation angles corresponding to the optical pixel signal emission angle; ranging logic means coupled to the decoder means for producing a target range corresponding to the global positioning system (GPS) coordinates for the gun with respect to GPS coordinates for the target; and simulation controller means coupled to the decoder means and the ranging logic means for producing a hit-miss decision representing the simulated ballistic projectile effects on the target.
 16. The PGS target assembly of claim 15 further comprising: an obturator disposed to selectively block reflection from the retroreflector means; and an obturator modulator coupled to the obturator for selectively reflecting an optical return window signal back along the line of incidence by opening and closing the obturator.
 17. The PGS target assembly of claim 16 further comprising: an encoder coupled to the obturator modulator for encoding the reflected optical return window signal according to a response code representing the simulated ballistic projectile effects on the target.
 18. The PGS target assembly of claim 15 further comprising: in the simulation controller means, means for producing simulated projectile impact coordinates corresponding to the target azimuth and elevation angles, the target range and the trigger pull time.
 19. The PGS target assembly of claim 15 further comprising: an optical transmitter for transmitting an optical signal; an encoder coupled to the optical transmitter for encoding the optical signal to represent the hit-miss decision; and a steering logic coupled to the optical transmitter for aiming the optical signal to illuminate the gun location corresponding to the optical pixel signal.
 20. The PGS transmitter assembly of claim 15 wherein the optical detector means has a field of view (FOV) of generally 360 degrees in azimuth and generally 45 degrees in elevation.
 21. A precision gunnery simulation (PGS) system for simulating the effects on a target of firing a ballistic projectile at a trigger pull time from a gun having a muzzle, the PGS system comprising: a PGS transmitter assembly comprising an optical transmitter fixed to the muzzle for emitting an optical pixel signal and an optical return window signal, a transmit controller coupled to the optical transmitter for encoding the optical pixel signal to represent its emission angle with respect to the muzzle and global positioning system (GPS) coordinates for the gun, a first optical detector fixed to the gun for receiving a reflected optical signal from the retroreflector, and a first decoder coupled to the first optical detector for recovering data from the reflected optical signal; and a PGS target assembly comprising a retroreflector for reflecting an incoming optical signal generally back along the incoming path thereof, a second optical detector for receiving an optical pixel signal encoded to represent its emission angle with respect to the muzzle and GPS coordinates for the gun, a second decoder coupled to the second optical detector for producing target azimuth and elevation angles corresponding to the optical pixel signal emission angle, a ranging logic coupled to the second decoder for producing a target range corresponding to the GPS coordinates for the gun with respect to GPS coordinates for the target, and a simulation controller coupled to the second decoder and the ranging logic for producing a hit-miss decision representing the simulated ballistic projectile effects on the target.
 22. The PGS system of claim 21 further comprising: in the PGS transmitter assembly, a scanning encoder coupled to the optical transmitter for encoding a sequence of optical pixel signals each emitted from the gun at one of a plurality of predetermined emission angles.
 23. The PGS transmitter assembly of claim 22 further including: in the PGS transmitter assembly, a beam number encoder coupled to the transmit controller for encoding the optical pixel signal with a sequential beam number corresponding to a predetermined angle with respect to the muzzle.
 24. The PGS transmitter assembly of claim 21 further including: in the PGS transmitter assembly, a trigger pull encoder coupled to the transmit controller for encoding the optical pixel signals to represent the trigger pull time.
 25. The PGS system of claim 21 wherein the optical transmitter emits infrared (IR) energy having a wavelength in the range from generally 1500 to generally 1600 nanometers.
 26. The PGS system of claim 21 further comprising: in the PGS target assembly, an obturator disposed for obstructing the retroreflector to prevent reflection thereby; and a controller coupled to the retroreflector obturator for selectively reflecting an optical return window signal back along the line of incidence by opening and closing the retroreflector obturator.
 27. The PGS system of claim 26 further comprising: in the PGS target assembly, an encoder coupled to the controller for encoding the reflected optical return window signal according to a response code representing the simulated ballistic projectile effects on the target.
 28. The PGS system of claim 21 further comprising: in the PGS target assembly simulation controller, logic for producing simulated projectile impact coordinates corresponding to the target azimuth and elevation angles, the target range and the trigger pull time.
 29. The PGS target assembly of claim 21 further comprising: in the PGS target assembly, an optical transmitter for transmitting an optical signal; an encoder coupled to the optical transmitter for encoding the optical signal to represent the hit-miss decision; and a steering logic coupled to the optical transmitter for aiming the optical signal to illuminate the gun location corresponding to the optical pixel signal.
 30. The PGS system of claim 21 wherein the second optical detector has a field of view (FOV) of generally 360 degrees in azimuth and generally 45 degrees in elevation. 